<template>
  <div class="list">
    <ul>
      <li class="item"
        v-for="(item) of letters"
        :key="item"
        :ref="item"
        @click="handlerLetterClick"
        @touchstart.prevent='handelTouchStart'
        @touchmove='handelTouchMove'
        @touchend='handelTouchEnd'
        >
        {{item}}</li>
    </ul>
  </div>
</template>
<script>
export default {
  name: 'CityAlphabet',
  props: {
    cities: Object
  },
  data () {
    return {
      touchStatus: false,
      startY: 0,
      timer: null
    }
  },
  updated () {
    this.startY = this.$refs['A'][0].offsetTop
  },
  computed: {
    letters () {
      const letters = []
      for (let i in this.cities) {
        letters.push(i)
      }
      return letters
    }
  },
  methods: {
    handlerLetterClick (e) {
      const val = e.target.innerText
      this.$emit('change', val)
    },
    handelTouchStart () {
      this.touchStatus = true
    },
    handelTouchMove (e) {
      if (this.touchStatus) {
        if (this.timer) {
          clearTimeout(this.timer)
        }
        this.timer = setTimeout(() => {
          const touchY = e.touches[0].clientY - 89
          const index = Math.floor((touchY - this.startY) / 20)
          if (index >= 0 && index < this.letters.length) {
            this.$emit('change', this.letters[index])
          }
        }, 16)
      }
    },
    handelTouchEnd () {
      this.touchStatus = false
    }
  }
}
</script>
<style scoped lang='stylus'>
@import '~styles/varibles.styl'
.list
  display: flex
  flex-direction:column
  justify-content: center
  position: absolute
  top:1.78rem
  right:0
  bottom:0
  width:0.4rem
  .item
    line-height: 0.4rem
    color: $bgColor
    text-align: center
</style>
